1. Field of the Invention
The present invention relates to a single chamber two-way servo-operated valve in accordance with the introduction to the main claim.
In the state of the art two-way servo-operated valves present a valving disc which closes a port and is keyed onto a stem controlled by an actuator which can be of separated chamber or single chamber type.
In separated chamber models the actuator comprises a rigid actuator disc with a connected diaphragm which is clamped onto the end of the actuator edge by a cover, to hence divide the actuator volume into a first chamber on one side of the actuator disc and a second chamber on the opposite side. The two chambers are completely separated from each other and from the fluid which flows through the valve. Normally the actuator disc is composed of two superposed discs keyed onto the stem, between them there being clamped the diaphragm which is holed in the centre for passage of the stem. In this manner the diaphragm is connected to the actuator disc and follows its movements by flexing. An actuator fluid enters one of the actuating chambers to control the movement of the actuator disc and of the valving element keyed onto the same stem.
The actuator fluid can be the same as that flowing through the valve and withdrawn upstream of its entry into the valve, but is generally a different fluid at higher pressure, to achieve a smaller-dimension actuator.
In single chamber valves there is only one actuating chamber defined by the inner surface of a cover, by a side of the actuator disc and by the flexible diaphragm connected to it, the edge of which is clamped between the cover and the valve body. The fluid to be intercepted by the valve flows on the other side of the actuator disc and acts on the actuator with its pressure. In this case the function of the actuator disc and of the valving disc can be performed by a single actuator/valving disc (hereinafter known simply as “disc”). It currently consists of two superposed discs keyed onto a stem, between them there being clamped a diaphragm holed in its centre for passage of the stem, its edge being clamped between the cover and the valve body to separate the actuating chamber from the fluid flowing through the valve, to enable the valving element to move with diaphragm flexure.
The fluid fed into the actuating chamber for valve operation is normally the same as that flowing through the valve, withdrawn upstream of the port to be closed by the valving element.
When the fluid withdrawn upstream of the port is fed into the actuating chamber it presses against the disc and, possibly aided by a spring or elastic member, closes the valving element by overcoming the pressure exerted by the fluid flowing through the valve on the other side of the disc, separated from the actuating chamber. To obtain movement in the opposite direction, the actuating chamber has merely to be emptied.
The stem normally emerges from the cover to visually indicate the valve opening or closure state. This reduces the active surface of the disc on the actuating chamber side.
Even though a single chamber valve represents a considerable constructional simplification compared with a double chamber valve, it still comprises a considerable number of component parts: a flexible diaphragm, an actuator/valving disc formed in two parts to clamp the diaphragm, a stem, a gasket for sealing the valving disc against the edge of the port to be closed, and a clamping element between the stem and discs.
The large number of parts also results in complicated assembly, resulting in longer times and possible errors.
2. Description of the Related Art
Simpler single chamber valves also exist in which the valving element is formed from a simple fabric-incorporated rubber diaphragm, with valving element inflexion for opening. However such valves cannot be used in applications in which the operating pressures are high, and also result in less precise operation, for which reason they are excluded from certain specifications.